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GCSE level physics exam revision notes
on thermal energy 1
Part 1.4
Thermal energy transfer
by thermal radiation (electromagnetic infrared radiation)
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INDEX for physics notes on thermal
energy transfer by conduction, convection and radiation
1.4
Thermal energy transfer
by thermal radiation (electromagnetic infrared radiation)
Thermal (heat) radiation
is emitted by all materials, gases, liquids or solids and the hotter the
material the more strongly it gives out heat radiation which is called
infrared radiation (IR).
-
(a) All objects continuously emit and absorb
infrared radiation from their surface, whatever their temperature
- increasing or decreasing their thermal energy stores.
-
(b) The higher the temperature (the hotter) an object
is, the more infrared radiation it radiates in a given time, the higher the
temperature of the material, the more intense is the infrared radiation.
-
An object that is hotter (higher
temperature) than its surroundings will emit more radiation than it absorbs
and an object that is cooler than its surroundings will absorb more
radiation than it emits.
-
You notice this effect in bright
sunlight by feeling the warmth on your hand or standing near a fire.
-
When an object cools down to the
same temperature as its surroundings emitted infrared radiation equals the
absorbed heat radiation.
-
-
(c)
Dark, matt surfaces
are good absorbers and good emitters of infrared radiation eg rough black
surfaces.
-
Solar panels for hot water
comprise of pipes carrying water to be heated set under a black surface to
efficiently absorb the infrared radiation from the Sun.
-
You can even just
use matt black painted water pipes.
-
You may even have a silvered surface
under the pipes so more infrared ins reflected onto the black surface rather
than becoming waste heat radiation.
-
The pipes are made of copper which
allows efficient conduction of the surface heat energy to the incoming cold
water., so the hot water can be used as part of the households domestic
heating or washing etc.
-
-
(d)
Light, shiny smooth surfaces are poor
absorbers and poor emitters of infrared radiation eg white gloss paint,
silver surface used in vacuum flask.
-
(e) Light, shiny surfaces are good reflectors
of infrared radiation, this maybe to keep heat in to keep things warm or to
minimise heat radiation in to keep things cool eg a vacuum flask.
-
(f)
Car
headlamp
(e) Another domestic case of infrared radiation!
Unlike 'modern' LED bulbs, 'old fashioned' filament bulbs emit quite a
bit of IR heat radiation.
You can detect this with a frosty car where
the central portion of the ice melts first on the transparent headlamp cover.
Filament bulbs only
convert ~10% of the electrical energy into visible light energy, most of the
rest is converted into infrared radiation.
The ice on the headlamp cover absorbs infrared
equivalent to the latent heat of fusion (melting) and changes the ice to liquid
water.
Energy store changes: The chemical
energy store of the battery decreases as it is converted into
electrical energy.
The electrical energy increases the thermal
energy store of the metal filament of the bulb.
The thermal energy
store of the filament decreases as it emits visible and infrared EM
radiation.
The absorbed EM radiation increases the thermal energy
store of the headlamp cover and ice - causing the latter to melt.
Eventually all the energy involved from the battery increases the
thermal energy store of the surroundings.
A 'green' note: If there is, and
its happening now in the UK and other countries, a change from
very inefficient filament light bulbs to very efficient low
energy LED light bulbs, there will be quite a reduction in the
domestic demand for electricity.
This reduced demand will help,
on closure fossil fuel power stations, reduce CO2
emissions, reducing the greenhouse effect, and allow renewable
energy resources to take over more of our electricity
generation.
Key points
Thermal energy transfer:
Thermal energy transfer by infrared radiation
Information
sources for Doc Brown's key points: IGCSE-GCSE physics are based on
textbooks & syllabus-specifications for students taking the UK AQA, Edexcel,
OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE
physics 9-1 level science examinations
A structured set of summary revision notes on
thermal energy transfer
by infrared radiation, tailored to the major UK GCSE/IGCSE
physics exam boards: WJEC, CCEA, CIE, AQA, Edexcel, and OCR.
Thermal Energy Transfer by Infrared Radiation
- Infrared radiation
is a form of electromagnetic radiation that transfers
thermal energy without needing particles - it can travel
through a vacuum.
- All objects emit,
absorb, and reflect infrared radiation depending
on their temperature and surface properties.
Core Academic Content Across Exam Boards about
thermal energy transfer by infrared radiation
| Concept |
Description |
| Definition |
Transfer of thermal energy via
electromagnetic waves (infrared) |
| Medium Required |
None - can travel through vacuum
(unlike conduction/convection) |
| Emission |
All objects above absolute zero emit
infrared radiation |
| Absorption & Reflection |
Dark, matte surfaces absorb/emits
well; light, shiny surfaces reflect more |
| Black Body Radiation |
Ideal emitter/absorber used in
theoretical models (especially AQA, CIE) |
| Temperature Link |
Higher temperature → more radiation
emitted (Stefan-Boltzmann Law) |
| Wavelength Link |
Higher temperature → shorter
wavelength emitted (Wien’s Law) |
| Examples |
Sun warming Earth, heat from a fire,
infrared heaters, thermal blankets |
All boards include this under
energy transfers by heating or waves and radiation.
AQA and CIE emphasize black body radiation and
temperature balance, while Edexcel and OCR explore surface
effects and practical investigations.
Student Exam Tips about thermal energy transfer by
infrared radiation
- Use diagrams:
Show how radiation travels from hot to cold objects without needing a
medium.
- Revise surface effects:
Know which materials are good/bad emitters and absorbers.
- Understand black body models:
Especially for AQA and CIE - link to temperature and emission.
- Practice comparisons:
Be ready to contrast radiation with conduction and convection.
- Apply real-world examples:
Think of radiators, foil blankets, and solar heating.
Common Misconceptions about thermal energy
transfer by infrared radiation
- “Radiation needs particles”:
It doesn’t - infrared radiation travels through space.
- “Only hot objects emit
radiation”: All objects emit some radiation; hotter ones emit more.
- “Shiny surfaces are good
emitters”: They’re actually poor emitters and good reflectors.
- Confusing infrared with visible
light: Infrared is invisible but can be felt as heat.
Keywords, phrases and learning objectives for
thermal (heat) energy transfer by
infrared radiation
Be able to describe and explain thermal (heat) energy transfer by thermal radiation
and know it is
electromagnetic radiation in the infrared radiation region.
Know the by comparison the relative emission and
absorption properties of different surfaces e.g. black matt rough
surface compare to a white or shiny smooth surface.
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energy transfer
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Revision notes on explaining examples
of thermal energy transfer by infrared radiation based on the syllabus-specifications
for students taking IGCSE/GCSE level physics examinations, summary
revision notes and key points on explaining examples of thermal energy
transfer by infrared radiation for students taking the AQA
igcse/gcse physics notes on explaining examples of thermal energy transfer by
infrared radiation, Edexcel gcse
physics notes on explaining examples of thermal energy transfer by
infrared radiation, OCR 21st century GCSE
physics notes on explaining examples of thermal energy transfer by
infrared radiation, OCR gateway
GCSE physics notes on explaining examples of thermal energy transfer
by infrared radiation, WJEC gcse physics notes on explaining
examples of thermal energy transfer by infrared radiation, CCEA
gcse physics notes on explaining examples of thermal energy transfer by
infrared radiation for students taking CIE Cambridge igcse
physics, exam revision notes on
explaining examples of thermal energy transfer by infrared radiation, useful for US grade 9-10 physics courses,
importance of different reflections &
absorptions of infrared radiation by different surfaces
in GCSE level physics, What you need to know about different reflections
& absorptions of infrared radiation by different surfaces for
GCSE level
physics,
Explaining the use of different reflections & absorptions of infrared
radiation by different surfaces knowledge in GCSE level physics, Examples of
different reflections & absorptions of infrared radiation by
different surfaces explained
when studying GCSE level physics, What is
significant about different reflections & absorptions of infrared
radiation by different surfaces, describing the theory of
different reflections & absorptions of infrared radiation by
different surfaces when studying
GCSE level physics, revision notes for different reflections &
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Notes on thermal
energy transfer by conduction, convection, radiation
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